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Kev-M's ASHP Performance

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Air Source Heat Pumps (ASHPs)

Last Post by Kev M 4 years ago

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Kev M

(@kev-m)

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Joined: 5 years ago

Posts: 1276

Topic starter 08/11/2021 7:23 am

I've started this new thread after starting this process off here

I've had the ASHP since April 2021. Some details of the process of choosing, installing, etc. are here

I'm doing this to see if I can make my ASHP run more efficiently. By that I mean more cheaply, while still keeping the house warm. I'm not unhappy with the system now; it does a really good job of heating the house and hot water but being cheaper and using less energy is always better.

My system is a 14kW Mitsubishi Ecodan running 15 radiators. It was all new at installation, specified via MCS heat loss calculations. The house is a 150m2 1990s bungalow. Heating requirement on EPC is about 20,000 kWh/year although I suspect that is an overestimate. I have two zones, controlled by ESI wireless thermostats. As recommended and set up by the supplier, I've been running the system on the weather compensation setting. I've also been using the thermostat to control the zone temps like you would with a gas boiler; turning them down at night and during the day and up in the morning and evening. In terms of comfort, the ASHP does this very well; it heats up the house remarkably quickly.

I have MMSP so I can see minute by minute energy consumed, radiator flow temps and outside temp. It's not quite working properly so I can't see energy delivered or COP.

The first step in my plan is to control the system using weather compensation and bypass the thermostats. But before I do that, this is how energy consumption looks using the thermostats and the weather compensation curve I was left with.

The two graphs are for 24 hrs 5/11/21. You can see the frost protection overnight, the thermostats kicking in morning and evening and the HW in the middle of the day. Definitely not the slow, steady output ASHPs are said to be suited to. Both power and flow temps are up and down a lot; on the other hand, it's using no power at all a lot of the time. Total ASHP energy consumed was 30.6kWh. The weather compensation curve is 50C flow at 0C and 20C flow at 20C.

This topic was modified 4 years ago by Kev M

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Kev M

(@kev-m)

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Topic starter 08/11/2021 7:41 am

First adjustment 7/11/21:

Thermostats set to manual and 30C (i.e. calling for heat all the time)

Weather compensation changed to this

This is 45C flow at -3C and 20C flow at 18C.

TRVs in bedroom turned down

My plan is to use the main controller to move this curve up or down until I find the right setting to keep the house at 20-21C. I'll then change the curve so that it works when set to zero. I'll leave settings for at leat 24 hours to let things settle down after changes.

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Kev M

(@kev-m)

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Topic starter 08/11/2021 7:51 am

Update 08/11/21.

Phew, it's hot!! House is about 23.5C. It's 4C outside and flow temp is about 36C. On the previous settings, flow temp would have been about 42C. Obviously still too high so will shift the curve down later on.

This post was modified 4 years ago 2 times by Kev M

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Brendon Uys

(@heacol)

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08/11/2021 8:44 am

@kev-m That is good news, I would shift it to -2 and try that. Because of the steady temperature, most of our customers run their systems with an internal temperature of 19.

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Jeff

(@jeff)

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08/11/2021 8:59 am

Posted by: @kev-m

Update 08/11/21.

Phew, it's hot!! House is about 23.5C. It's 4C outside and flow temp is about 36C. On the previous settings, flow temp would have been about 42C. Obviously still too high so will shift the curve down later on.

Do you know how the energy consumption looked vs your previous post of 30.6kWh before any changes?

Appreciate no two days are the same so comparisons need to be taken with a pinch of salt.

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Kev M

(@kev-m)

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Topic starter 08/11/2021 11:19 am

@jeff, it's a bit early to say. I'll compare when I have 24 hrs; this time tomorrow.

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Kev M

(@kev-m)

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Topic starter 08/11/2021 9:15 pm

Update; I moved the compensation curve down -2 at 6pm. The house is still 22C or so. I'm aiming for 20-21 but I'll leave it like this for 24 hours. The ASHP is now firing up for about 10 minutes every 20 minutes or so, on low power. From what I have read, that's OK. The radiators are barely warm to the touch but are still convecting; flow temp is about 30. I'll post some graphs and numbers tomorrow.

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Brendon Uys

(@heacol)

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09/11/2021 7:27 am

@kev-m getting there, but will be better when you change the valves. Flow temp dropped from 43 to 30 and the house is still too hot. COP at 30 - round about 7at this ambient temperature. You obviously have a well-designed system, just not run properly.

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Kev M

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Topic starter 09/11/2021 7:40 am

Thanks Brendan.

Update - House is now 21.5C, feels just about right. Before, it would have been 18C and the heating would just have started after the night turned off. Apart from anything else, the house is much more pleasant like this. Flow temps are now only 27C at about 12C ambient.

I'm off to the gym now; I'll do some graphs/figures later.

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